Nonlinearity parameter for tissue-mimicking materials.

A finite amplitude insert-substitution method has been used to determine the ultrasonic nonlinearity parameter B/A of nine versions of water-based, macroscopically uniform ultrasonically tissue-mimicking (TM) nonfat and fat materials. In this method, the amplitude of the second harmonic following transmission through degassed distilled water with known B/A (B/A = 5.2) and the amplitude of the second harmonic following transmission through the unknown sample are measured. The ratio of these amplitudes allows calculation of the B/A of the sample. Measured B/A values of the nonfat materials range from 5.6 to 6.6. These values compare favorably with published values for nonfat soft tissues. In contrast, the measured B/A values for two tissue-mimicking fat materials are 9.8 and 11.1; these two values represent the low and high end of B/A for most fresh fatty tissues. For comparison, B/A was measured for two commonly available uniform materials, corn oil and ethylene glycol, and the results are in good agreement with published values.